1. Field of the Invention
The invention relates to an apparatus for cooling the coolant of the cooled gas turbine of a gas-turbine and steam-turbine plant; the latter comprises a waste-heat steam generator downstream of the gas turbine with heating surfaces which are connected into a water/steam loop of the steam turbine, and in which a first heat exchanger provided for cooling the coolant is linked to the secondary side of a second heat exchanger.
A gas-turbine and steam-turbine plant of this type is conventionally used for generating electrical energy. The aim is to provide an especially high temperature of the working medium at the inlet of the turbine of, for example, 1200.degree. to 1500.degree. C. so as to increase the power capacity of the gas turbine and therefore to achieve the highest possible efficiency. However, such a high turbine-inlet temperature entails material problems especially in respect of the heat resistance of the turbine blades.
2. Description of the Related Art
An increase in the turbine-inlet temperature is acceptable when the turbine blades are cooked to such an extent that they always have a temperature below the rated temperature limit of the turbine blade material. It has been known heretofore, for this purpose, from European patent specification EP 0 379 880 to branch off air compressed in a compressor assigned to the gas turbine and to cool the air serving as a coolant before the entry thereof into the gas turbine. It has also become known from European patent specification EP 0 519 304 A1 to use an air/water cooler for this purpose, by means of which the heat obtained during the cooling of the coolant is supplied to the water/steam loop via feed water used for this purpose. A disadvantage of this, however, is the increased outlay with respect to measurement and regulatory control, especially with regard to maintaining the necessary pressure and setting the quantity of the feed water extracted from the water/steam loop for coolant cooling. It has also become known from British Patent 2 264 539 A to transfer the heat obtained in cooling the coolant via an intermediate circuit to the feed water of the water/steam loop.